High resolution low power consumption OLED display with extended lifetime

ABSTRACT

Arrangements of pixel components that allow driving three or less of four or more sub-pixels to emit an original color signal are disclosed. A first projection of the original color signal may be projected onto the two sub-pixel&#39;s color space. The first projection may then be projected onto a second projection corresponding to the color space of a third pixel. The third pixel may be driven based on the second projection only two of the remaining at least three sub-pixels may be driven based on the third pixel being driven.

PRIORITY

This application is a non-provisional of U.S. Patent Application Ser.No. 62/003,269, filed May 27, 2014. This application is also acontinuation-in-part of U.S. application Ser. No. 14/243,145, filed Apr.2, 2014, which is a continuation-in-part of U.S. application Ser. No.13/744,581, filed Jan. 18, 2013, the disclosure of each of which isincorporated by reference in its entirety.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to light emitting devices such as OLEDdevices and, more specifically, to devices that include full-color pixelarrangements that have sub-pixels that emit not more than two colorsand/or incorporate not more than two color filters.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule istris(2-phenylpyridine)iridium, denoted Ir(ppy)3, which has the followingstructure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between. As used herein, two layers or regions may bedescribed as being disposed in a “stack” when at least a portion of onelayer or region is disposed over at least a portion of the other.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

Layers, materials, regions, and devices may be described herein inreference to the color of light they emit. In general, as used herein,an emissive region that is described as producing a specific color oflight may include one or more emissive layers disposed over each otherin a stack.

As used herein, a “red” layer, material, or device refers to one thatemits light in the range of about 580-700 nm; a “green” layer, material,or device refers to one that has an emission spectrum with a peakwavelength in the range of about 500-600 nm; a “blue” layer, material,or device refers to one that has an emission spectrum with a peakwavelength in the range of about 400-500 nm. In some arrangements,separate regions, layers, materials, or devices may provide separate“deep blue” and a “light blue” light. As used herein, in arrangementsthat provide separate “light blue” and “deep blue”, the “deep blue”component refers to one having a peak emission wavelength that is atleast about 4 nm less than the peak emission wavelength of the “lightblue” component. Typically, a “light blue” component has a peak emissionwavelength in the range of about 465-500 nm, and a “deep blue” componenthas a peak emission wavelength in the range of about 400-470 nm, thoughthese ranges may vary for some configurations. Similarly, a coloraltering layer refers to a layer that converts or modifies another colorof light to light having a wavelength as specified for that color. Forexample, a “red” color filter refers to a filter that results in lighthaving a wavelength in the range of about 580-700 nm. In general thereare two classes of color altering layers: color filters that modify aspectrum by removing unwanted wavelengths of light, and color changinglayers that convert photons of higher energy to lower energy.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

Pixel arrangements for light emitting devices are provided, whichinclude sub-pixels that emit not more than two colors and/or not morethan two color altering layers. Multiple sub-pixels within a full-colorpixel arrangement may emit the same color light initially, which is thenconverted to one or more other colors by various color filtertechniques.

According to an embodiment, a full-color pixel arrangement for an OLEDdevice includes a plurality of sub-pixels, each of which includes anemissive region. The arrangement may include emissive regions that emitlight of not more than two colors, and may include not more than twocolor altering layers. Each color altering layer may be disposed in astack with an emissive region associated with a sub-pixel. Thesub-pixels, and/or the corresponding emissive regions, may havedifferent physical sizes, and each emissive region may include one ormore emissive devices, layers, or materials.

In an embodiment, a full-color pixel for an OLED device may include aplurality of sub-pixels, including a first sub-pixel having an emissiveregion configured to emit blue light and a second sub-pixel having anemissive region configured to emit yellow light. The pixel arrangementmay include emissive regions of not more than two colors, and/or notmore than two color altering layers.

According to an embodiment, a full-color pixel arrangement for an OLEDdevice may include first, second, and third sub-pixels. The first regionmay be configured to emit a first color, and the second and thirdregions each configured to emit a second color. A color altering layermay be disposed in a stack with the second and/or the third emissiveregion. The arrangement also may include a fourth sub-pixel having anemissive region configured to emit the second color. A third coloraltering layer, which may provide a color different than those disposedin a stack with the second and/or third emissive regions, also may bedisposed in a stack with the fourth emissive region.

In an embodiment, a full-color OLED pixel arrangement may be fabricatedby depositing a first emissive material through a mask over a substrate,and depositing a second emissive material through a mask over thesubstrate, where the second emissive material is configured to emit adifferent color than the first emissive material. A first color filtermay be disposed in a stack with a portion of the second emissivematerial. In an embodiment, not more than two masking steps may be usedto fabricate the arrangement.

According to an embodiment, a display pixel including at least foursub-pixels may be driven. A first projection of an original color signalonto a color space maybe defined by a first and second sub-pixel of thefour sub-pixels. A second projection of the first projection onto asecond color space defined by a third sub-pixel may be determined. Thethird sub-pixel may be driven based on the magnitude of the secondprojection. Here, the third sub-pixel may emit a color equivalent to acombination of colors emitted by the first and second sub-pixels. Thesecond sub-pixel may be driven based on the difference between the firstprojection and the second projection. The fourth sub-pixel may be drivenbased on a component of the original color signal. The first sub-pixelmay not be activated while driving the third sub-pixel based on themagnitude of the second projection and driving the second sub-pixelbased on the difference between the first projection and the secondprojection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows a schematic illustration of an example masking arrangementsuitable for fabricating a pixel arrangement as disclosed herein.

FIG. 4 shows a schematic illustration of a pixel arrangement accordingto an embodiment disclosed herein.

FIG. 5 shows a schematic illustration of a pixel arrangement accordingto an embodiment disclosed herein.

FIG. 6 shows a schematic illustration of a pixel arrangement accordingto an embodiment disclosed herein.

FIG. 7 shows a schematic illustration of an example masking arrangementsuitable for fabricating a pixel arrangement as disclosed herein.

FIG. 8 shows a schematic illustration of a pixel arrangement accordingto an embodiment disclosed herein.

FIG. 9 shows a schematic illustration of an example masking arrangementsuitable for fabricating a pixel arrangement as disclosed herein.

FIG. 10 shows a schematic illustration of a pixel arrangement accordingto an embodiment disclosed herein.

FIG. 11 shows the 1931 CIE diagram that highlights a set of pointsoutside the RG line according to an embodiment disclosed herein.

FIG. 12 shows the 1931 CIE diagram with coordinates for pure red, green,and blue, and for a multi-component yellow source that lies outside theRG line according to an embodiment disclosed herein.

FIG. 13 illustrates an example color point rendered without the use of ared sub-pixel according to an embodiment disclosed herein.

FIG. 14 shows a CIE diagram that identifies red, green, blue, and yellowpoints, an established white point, and various color regions accordingto an embodiment disclosed herein.

FIG. 15 shows a schematic illustration of a pixel arrangement includinga blue color change layer disposed over a blue emissive region accordingto an embodiment disclosed herein.

FIG. 16 shows a schematic illustration of a pixel arrangement includinga blue color change layer disposed over a blue emissive region accordingto an embodiment disclosed herein.

FIG. 17 shows a schematic illustration of a pixel arrangement includinga blue color change layer disposed over a blue emissive region accordingto an embodiment disclosed herein.

FIG. 18 shows a diagram that identifies red, green, blue and yellowpoints and associated color spaces, according to an embodiment disclosedherein.

FIG. 19 shows another diagram that identifies red, green, blue andyellow points and associated color spaces, according to an embodimentdisclosed herein.

FIG. 20a shows a color space defined by two sub-pixels, according to anembodiment disclosed herein.

FIG. 20b shows a color space defined by a single sub-pixel, according toan embodiment disclosed herein.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink jet and OVJD. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, medical monitors, televisions,billboards, lights for interior or exterior illumination and/orsignaling, color tunable or color temperature tunable lighting sources,heads up displays, fully transparent displays, flexible displays, laserprinters, telephones, cell phones, personal digital assistants (PDAs),laptop computers, digital cameras, camcorders, viewfinders,micro-displays, vehicles, a large area wall, theater or stadium screen,or a sign. Various control mechanisms may be used to control devicesfabricated in accordance with the present invention, including passivematrix and active matrix. Many of the devices are primarily intended foruse in a temperature range comfortable to humans, such as 18 degrees C.to 30 degrees C., and more preferably at room temperature (20-25 degreesC.), but can operate at temperatures outside this range, such as −40 Cto +85 C or higher.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

Current display architectures and manufacturing capabilities typicallydo not allow for low power consumption and high resolution OLEDdisplays. For example, side by side (SBS) architecture typically canachieve relatively low power consumption (and therefore good lifetime),but this architecture may require relatively high resolution shadowmasking. Such techniques often are limited to around 250 dpi resolution.To achieve higher resolutions, architectures using white devices inconjunction with color filters may be used to avoid patterning the OLEDemissive layers. However, such techniques typically suffer fromrelatively lower efficiency and therefore higher power consumption,which also reduces lifetime. These constraints may be somewhat overcomeby employing a RGBW pixel architecture that uses both an unfilteredwhite sub-pixel and devices that emit at individual colors by employingcolor filters over other white sub-pixels. This architecture generallyis considered to result in poorer image quality, and typically still hasa lower power consumption and poorer lifetime than a comparable RGB SBSdisplay.

The present disclosure provides arrangements of pixel components thatallow for full-color devices, while using emissive devices that emit notmore than two colors, and/or a limited number of color altering layers.Embodiments disclosed herein may provide improved performance overconventional RGBW displays, such as lower power consumption and longerlifetime, with fewer high resolution masking steps, and at a lowerresolution, in comparison to a conventional RGB SBS display That is,although an arrangement as disclosed herein may include any number ofsub-pixels or other emissive devices or regions, within the arrangementthere may be a limited number of colors emitted by emissive devices orregions within the arrangement. As a specific example, an arrangement asdisclosed herein may include three sub-pixels. Two of the sub-pixels mayinclude emissive regions, such as OLEDs, that emit light of the samecolor, with one of the sub-pixels being filtered or otherwise modifiedto produce a different color after light is emitted by the emissiveregion. The third sub-pixel may include an emissive region that emitslight of a different color than the first emissive regions within thetwo sub-pixels. Thus, although the sub-pixels overall may produce lightof three or more colors, the emissive regions within the arrangementneed only initially emit light of two colors. Devices disclosed hereinalso may be achieved using simplified fabrication techniques compared toconventional SBS arrangements, because fewer masking steps may berequired.

In an embodiment, two masking steps may be used. This may provide forsimplified fabrication when compared to the three masking steps requiredfor a conventional RGB SBS display. Each mask opening area may beapproximately half the pixel area, as opposed to a third in aconventional SBS display. The increased area of the shadow mask openingrelative to a conventional SBS display of the same pixel size may allowfor higher pixel density. For example, the same size opening will allowfor up to about a 50% increase in display resolution compared to aconventional SBS technique. In some configurations, the exact size ofthe mask openings may be determined based upon lifetime matchingconsiderations, such as to optimize current flow through each sub-pixeland thus improve overall display lifetime.

An increase in fill factor also may also be possible using techniquesdisclosed herein, particularly for top emitting AMOLED displays, whichmay allow for higher efficiency relative to a conventional three-maskpixilation approach of the same resolution. This is due to therelatively increased area of the three sub-pixels in a two-mask approachas disclosed, compared to a conventional three-mask approach. With atwo-mask approach as disclosed, less current may be required for atleast some sub-pixels, to render the same luminance from a display. Thismay result in higher device efficiency, lower voltage, and/or longerdisplay lifetime.

FIG. 3 shows a schematic illustration of an example masking arrangementsuitable for fabricating a pixel arrangement as disclosed herein. In afirst masked deposition, an emissive layer structure, or a stackeddevice structure including multiple emissive layers, may be deposited ina first region 310. The first region contains one or more emissivelayers that emit light of a first color. A second masked deposition maybe performed in an adjacent or otherwise nearby region 320, to depositan emissive layer or stacked structure that emits light of a secondcolor different from the first. Two color altering layers 330, 340, maythen be disposed over the second emissive region, such that lightpassing through each filter may be converted from the second color tothird and fourth colors, respectively, each different from the first andsecond. In some configurations, a portion of the second emissive regionmay be left uncovered, such that the illustrated arrangement may providelight having four distinct colors. In some configurations, the coloraltering layers 330, 340 may cover the entirety of the second region,such that the illustrated arrangement provides light of three distinctcolors. Although shown as disposed with some distance between them inFIG. 3 for illustration purposes, it will be understood that in generalthe color filters may be disposed immediately adjacent to one another,such that no yellow light is emitted in the region between the filters.Similarly, each filter may extend to the appropriate edges of the yellowemissive region, such that no yellow light is emitted from the edgeimmediately adjacent to the color altering layer. Each of the emissivelayers or stacked structures may include one or more emissive materials,each of which may be phosphorescent or fluorescent. More generally, eachemissive material may include any of the emissive materials, layers,and/or structures disclosed herein.

As a specific example, the first mask deposition 310 may provide a bluedevice, which may be a single EML structure or a stacked devicecontaining more than one EML. As is known in the art, a stacked devicemay be desirable to provide extended lifetime and/or reduced imagesticking; in other arrangements, a single-layer emissive device may bepreferred to reduce fabrication cost and complexity. The blue OLED maybe phosphorescent or fluorescent. The second mask deposition 320 mayprovide a yellow device, which may be made, for example, by combiningred and green emitters. More generally, the yellow device may beprovided using any suitable combination of emissive materials and/orlayers. As specific examples, separate red and green emitters may beprovided in one mixed layer; in separate layers within a two-EML device;in a stacked device with a red EML in one OLED within the stack and agreen EML in the other; in a yellow device using a single EML containinga yellow emitter; or in a stacked device containing two yellow EMLs.Thus, in some configurations, an emissive region may be provided bymultiple emissive materials, each of which has an emission spectrum orpeak emission wavelength that differs from the ultimate color of theregion as a whole. Various combinations also may be used, thoughadvantageously any selected combination may be deposited using the samesecond mask arrangement. In the completed example configuration, theblue device is controlled by one anode and associated active matrixcontrol circuit. The yellow device is divided into three sub-pixels,yellow, green and red. Each sub-pixel is then controlled by its ownanode and associated active matrix control circuit. The yellow sub-pixeluses the unfiltered yellow light from the yellow OLED. The greensub-pixel is obtained by placing a green color filter over the yellowOLED, and, similarly, a red sub-pixel is obtained by placing a red colorfilter over the yellow OLED. Thus, the resulting pixel arrangement hasfour sub-pixels, red, green, blue, and yellow (RGBY). Such anarrangement may be advantageous, because the blue performance may not belimited by a color filter as in a conventional RGBW display, but mayhave the same optimized lifetime as in a conventional RGB SBS display.Further, in a conventional RGBW arrangement, the green color filter isconfigured to prevent transmission of as much blue and red light aspossible. Thus, a band-pass filter typically is used as the green colorfilter. In an RGBY arrangement as disclosed herein where yellow light isused as a multi-component light source, the green color filter may beconfigured to prevent transmission only of red light since themulti-component light does not include a blue component. Thus, a cut-offfilter may be used instead of a band-pass filter, which may providerelatively greater efficiency and color saturation.

Embodiments disclosed herein may use unfiltered yellow light to improvedisplay efficiency at times when highly saturated red or green is notrequired. In operation, the unfiltered yellow device may be used in asimilar manner to white in conventional a RGBW display, and similaralgorithms may be employed for signal processing. To render a specificunsaturated color, yellow light can be mixed with the three individualprimary red, green or blue colors, which may provide higher efficiencythan just using the red, green or blue primary colors alone. Afull-color display using this technique may have only about a 12% higherpower consumption than a conventional SBS RGB arrangement, in contrastto a conventional RGBW arrangement which typically has about a 50%higher power consumption than the SBS RGB arrangement. This level ofpower reduction may be achieved even if the overall red and greensub-pixel efficiency is reduced by 25%. For example, color filters mayreduce the efficiency for the red and green alone by 50%, but theunfiltered yellow sub-pixel may restore much of this loss.

Embodiments disclosed herein similarly may allow for increased displaycolor range. For example, referring to FIG. 11, a yellow multi-componentsource may be configured such that it emits light having CIE coordinatesthat lie on the “RG line” between the identified pure red and greenpoints, such as the illustrated point 1104. In some embodiments, theidentified red and green points may correspond to the “pure” colorsemitted by emissive regions in the corresponding sub-pixels.Alternatively, the yellow multi-component source may be configured toemit light that lies outside the RG line, such as point 1108, any pointalong the illustrated curve 1100, or the like. The use of such amulti-component source may increase the available display color gamut,by allowing for use of the CIE region outside the RG line. The increasein color gamut may be achieved or used when the yellow multi-componentsource is filtered to provide red and/or green light, or it may be usedwhen the yellow source is used unfiltered, according to the variousarrangements disclosed herein. Thus, in some configurations, it may bedesirable for the yellow multi-component source to have CIE coordinatesthat lie outside the RG line on the 1931 CIE diagram.

FIG. 4 shows a schematic illustration of a pixel arrangement accordingto an embodiment disclosed herein. As described with respect to FIG. 3,the arrangement includes four sub-pixels 410, 420, 430, 440. Onesub-pixel 410 includes one or more emissive devices or regions that emitlight of a first color. The other sub-pixels 420, 430, 440 areconstructed using emissive regions that emit light of a second color. Acolor altering layer 432, 442 may be disposed over each of two of theemissive regions 434, 444. The third sub-pixel 420 is left unfiltered,resulting in a pixel arrangement that has four sub-pixels, eachproviding light of a different color.

In some configurations, additional color altering layers may be used.For example, a blue color altering layer may be disposed over the blueemissive region 410 to modify the spectral output resulting at the bluesub-pixel. An example of such a configuration is shown in FIG. 15, inwhich a blue color altering layer is disposed over the blue emissiveregion, while the other emissive regions and color altering layers arethe same as shown in FIG. 4. Although shown generally as a blue coloraltering layer and a blue emissive region for clarity, the blue coloraltering layer may be a light blue or deep blue color altering layer.Similarly, the blue emissive region may be a deep blue or light blueemissive region.

As described with respect to FIG. 3, each sub-pixel may be controlled byan associated control circuit. Example control circuits are shown inFIG. 4 for purposes of illustration, with various control elementsshaded to match the controlled emissive regions. The specificarrangement of control circuitry is provided by way of example only, andany suitable control circuitry may be used as will be readily apparentto one of skill in the art.

In general parlance in the art, a “sub-pixel” may refer to the emissiveregion, which may be a single-layer EML, a stacked device, or the like,in conjunction with any color altering layer that is used to modify thecolor emitted by the emissive region. For example, the sub-pixel 430includes an emissive region 434 and a color altering layer 432. As usedherein, the “emissive region” of a sub-pixel refers to any and allemissive layers, regions, and devices that are used initially togenerate light for the sub-pixel. A sub-pixel also may includeadditional layers disposed in a stack with the emissive region thataffect the color ultimately produced by the sub-pixel, such as coloraltering layers disclosed herein, though such color altering layerstypically are not considered “emissive layers” as disclosed herein. Anunfiltered sub-pixel is one that excludes a color modifying componentsuch as a color altering layer, but may include one or more emissiveregions, layers, or devices.

In some configurations, fewer sub-pixels may be used to achieve afull-color device or pixel arrangement. FIG. 5 shows an examplearrangement that uses three sub-pixels 510, 520, 530. Similarly to theexample shown in FIG. 4, a first sub-pixel 510 may be created bydepositing one or more emissive regions through a mask, in a singleemissive layer or a stacked arrangement, and leaving the resultingsub-pixel unfiltered. The other two sub-pixels 520, 530, may bedeposited during a single masked deposition. As previously described,each may include one or more emissive materials and/or layers, and maybe individual emissive layers or stacked devices. A color altering layer532 may then be disposed over one or more of the emissive regions, toresult in a full-color arrangement having three sub-pixels of differentcolors.

As a specific example, the two masking steps may be blue and green. Thatis, in a first masked deposition technique, a blue layer or stack may bedeposited in a region corresponding to the first sub-pixel 510. Greenlayers or stacked devices may be deposited in regions corresponding tothe second and third sub-pixels 520, 530 in a second masked deposition.The green sub-pixel 520 provides unfiltered green light. The redsub-pixel 530 uses a color altering layer 532, such as a green-to-redcolor changing layer having a relatively high conversion efficiency, toconvert the green light emitted by the green device 530 to red light.Such a configuration may result in a display that with up to 50% higherresolution than a comparable conventional RGB SBS display, with littleor no increase in power consumption or associated decrease in lifetime.Such an approach also may improve the display efficiency by not “losing”as much light due to use of a conventional color filter, instead using acolor changing layer to provide the third color.

As another example, a blue color altering layer may be disposed over theblue emissive region as previously described. Such a configuration isshown in FIG. 16. As previously described, the blue color altering layermay be a light blue or deep blue color altering layer, and the blueemissive region may be a deep blue or light blue emissive region.

FIG. 6 shows a schematic illustration of a configuration in which thetwo masking steps are blue and yellow, i.e., one or more blue emissivelayers are deposited during one masked deposition, and one or moreyellow emissive layers are deposited during another. As with FIG. 6, theillustrated configuration uses only three sub-pixels, red, green, andblue. In this example, the green sub-pixel uses a green color filter toconvert light from the yellow OLED to green, the red sub-pixel uses ared color filter to convert light from the yellow OLED to red, and theblue sub-pixel uses unfiltered light from the blue OLED. Similarconfigurations may use color altering layers other than or in additionto the specific color filters shown.

As another example, a blue color altering layer may be disposed over theblue emissive region as previously described. Such a configuration isshown in FIG. 17. As previously described, the blue color altering layermay be a light blue or deep blue color altering layer, and the blueemissive region may be a deep blue or light blue emissive region.

In some configurations, the efficiency of one or more sub-pixels may beenhanced by using a color changing layer instead of, or in addition to,a conventional color filter as a color altering layer as disclosedherein. For example, referring to the example shown in FIG. 6, a redcolor changing layer with a relatively high conversion efficiency fromyellow to red may be placed between the yellow OLED and red colorfilter. Such a configuration may enhance the red sub-pixel efficiency.More generally, the use of a color changing layer disposed in a stackwith an OLED, or an OLED and a color filter, may enhance the efficiencyof that sub-pixel.

Other configurations disclosed herein may use additional color alteringlayers, and may include color altering layers disposed over multipleemissive regions or types of emissive region. FIG. 7 shows an examplemasking arrangement that uses emissive regions of two colors, light blue710 and white 720. The masked areas may be used to deposit emissiveregions of each color as previously disclosed. Various color alteringlayers also may be disposed over the resulting emissive regions tocreate a full-color pixel arrangement. In the example shown in FIG. 7, adeep blue color filter 730, a red color filter 740, and a green colorfilter 750 are disposed over corresponding white emissive regions, toform three sub-pixels of those colors, while the light blue emissiveregion remains unfiltered to form a light blue sub-pixel. Such aconfiguration may be used to enhance overall blue lifetime by using thelight blue and deep blue sub-pixels as needed, as described in U.S.Patent Publication No. 2010/0090620, the disclosure of which isincorporated by reference in its entirety. As previously described,other color altering layers may be used in addition to or instead of thespecific color filters described with respect to FIG. 7.

FIG. 8 shows an example pixel arrangement corresponding to thedeposition arrangement shown in FIG. 7. Similarly to the arrangementshown in FIG. 4, the arrangement of FIG. 7 includes an unfilteredsub-pixel 810, and three sub-pixels 820, 830, 840 each of which isformed from an emissive region 821, 831, 841 and a color filter 822,832, 842, respectively. In the example shown in FIG. 7, the unfilteredsub-pixel 810 is a light blue sub-pixel, and the color filters 822, 832,842 are deep blue, red, and green, respectively. The specific emissioncolors and color filters shown are illustrative only, and various othercolors, color altering layers, and combinations may be used withoutdeparting from the scope of embodiments disclosed herein.

In an embodiment, each emissive region deposited during each of twomasked deposition operations may be combined with a color altering layerto form one or more pixels. FIG. 9 shows an example arrangement in whicheach type of emissive region is combined with one or more color alteringlayers to create multiple sub-pixels. For example, the two maskedregions may correspond to a light blue emissive region 910 and a yellowemissive region 920, each of which may be deposited in one of twomasking steps as previously described. A deep blue color altering layer930 may be combined with a light blue emissive region 910 to form a deepblue sub-pixel. Red and green color altering layers 930, 940,respectively, each may be combined with a portion of a yellow emissiveregion to form red and green sub-pixels. A light blue emissive regionalso may be left unfiltered to form a light blue sub-pixel. As describedwith respect to FIG. 7, use of the light and deep blue sub-pixels mayimprove performance and device lifetime. In addition, the relativelylong light blue lifetime can extend overall display operation andprovide improved power efficiency, since the light blue sub-pixel isunfiltered.

FIG. 10 shows a pixel arrangement corresponding to the mask and coloraltering layer arrangement described with respect to FIG. 9. As shown,four sub-pixels are created from two emissive regions of a first color,one of which is unfiltered, and two emissive regions of a second color.Following the example of FIG. 9, a light blue sub-pixel is formed froman unfiltered light blue emissive region, a deep blue sub-pixel isformed from a light blue emissive region and a deep blue color alteringlayer, a red sub-pixel is formed from a yellow emissive region and a redcolor altering layer, and a green sub-pixel is formed from a yellowemissive region and a green color altering layer. The specific emissioncolors and color altering layers shown are illustrative only, andvarious other colors, color altering layers, and combinations may beused without departing from the scope of embodiments disclosed herein.

Embodiments of the invention disclosed herein may use a variety of driveschemes. In many embodiments, four sub-pixels may be available to rendereach color. Typically, only three sub-pixels may be needed to render aparticular color; thus there are multiple options available for theelectrical drive configuration used to render the color. For example,FIG. 12 shows the 1931 CIE diagram with coordinates for pure red, green,and blue, and for a multi-component yellow source that lies outside theRG line according to an embodiment disclosed herein. In a four sub-pixelarrangement as disclosed herein, when rendering a color in the GBY space1210, the red sub-pixel is not required; similarly, if the color to berendered is within the RBY space 1220, the green sub-pixel is notrequired. FIG. 13 illustrates an example color point rendered withoutthe use of a red sub-pixel, i.e., a point which lies within the GBYspace 1210 in FIG. 12. As shown the initial contribution of pixels forthe example point may be R₀, G₀, B₀ for the red, green, and bluesub-pixels, respectively, in a RGBY arrangement. In an RGBY arrangementas disclosed herein, the equivalent contributions for yellow, green, andblue sub-pixels may be Y′, G′, B′, respectively. Notably, the redsub-pixel need not be used to render the desired color.

Another drive arrangement according to embodiments disclosed herein isto fix a white point using yellow and blue sub-pixels. A desired colormay then be rendered through use of the green or red sub-pixel,depending on whether the color lies within the GBY or RBY space. FIG. 14shows a CIE diagram that identifies red, green, blue, and yellow pointsas previously disclosed. A white point 1404 may be established along theBY line using a combination of only the blue and yellow sub-pixels, asshown. A color point 1400 falling in the GBY space, i.e., on the greenside of the BY line, thus may be rendered by using the green sub-pixelin addition to the blue and yellow sub-pixels. Similarly, a point in theBYR space, i.e., on the red side of the BY line, may be rendered usingthe blue, yellow, and red sub-pixels. Thus, embodiments disclosed hereinallow for a variety of drive arrangements, and may provide additionalflexibility, efficiency, and color range compared to conventional RGBWand similar arrangements.

An emissive region, layer, or device disclosed herein may be asingle-layer emissive layer, or it may be a stacked device. Eachemissive region, layer, or device may also include multiple emissivematerials which, when operated in conjunction, provide the appropriatecolor light for the component. For example, a yellow emissive region mayinclude both red and green emissive materials in an appropriateproportion to provide yellow light. Similarly, any emissive region ordevice may be a stacked device or otherwise include emissive sub-regionsof sub-colors that are used to provide the desired color for the regionor device, such as where a stacked configuration with red and greendevices is used to provide a yellow emissive region. Each also mayinclude multiple emissive materials that provide light of the same coloror in the same region. Further, each emissive material used in any ofthe configurations disclosed herein may be phosphorescent, fluorescent,or hybrid, unless indicated specifically to the contrary. Although asingle emissive region as disclosed herein may include multiple emissivematerials, it may be described as emitting only a single color, sincetypically it will not be configured to allow for only one of theemissive materials to be used. For example, a yellow emissive region mayinclude both red and green emissive materials. Such a region isdescribed herein as a yellow emissive region and is considered asingle-color emissive region, since the red and green emissive materialscannot be activated independently of one another.

According to embodiments of the disclosed subject matter, a pixelincluding at least four sub-pixels may be driven based on projectionsassociated with a color signal. The sub-pixels may correspond to orinclude emissive regions containing two or fewer colors, such as a blueemissive region and a yellow emissive region. Multiple sub-pixels may beformed from a single emissive region as previously described, such as bythe use of color altering layers optically coupled to portions of one ofthe sub-pixels. Such a pixel arrangement may include no more than twocolor altering layers.

In operation, a color signal that defines or otherwise provides anintended color to be generated by the pixel is used to drive the pixel.As an example, a display containing thousands of pixels may beconfigured to display an image of an automobile at a given time. Aparticular pixel may be located in an area of the display such that, todisplay the automobile, the intended color output by the pixel is anorange represented by the hex value #FFA500. Instead of driving all foursub-pixels, three of the four sub-pixels may be driven such that thelight that would have been emitted by a primary color sub-pixel in aconventional display (e.g., a green sub-pixel) may be emitted instead bya secondary color pixel (e.g., a yellow sub-pixel). Further, of thethree of four sub-pixels that are driven, a primary color sub-pixel(e.g., a red sub-pixel) may be driven at a lower magnitude based on asecondary sub-pixel (e.g., the yellow sub-pixel) emitting a portion ofthe light that the primary color sub-pixel (e.g., red sub-pixel) wouldhave emitted if driven without the secondary sub-pixel.

As disclosed herein, a color space may be defined by one or moresub-pixels. A color space may correspond to the range of colorsavailable based on the color emission range of one or more sub-pixels.An example of a three sub-pixel color space is shown in FIG. 18. Thethree axes (Red, Blue, and Green) represent the color space availablebased on the three respective red, blue, and green sub-pixels, as shownby the box 1800. Notably, any color point within the color space box1800 may be emitted by driving the Red, Blue, and Green sub-pixels atlevels corresponding to the projection of the color point onto eachrespective sub-pixel. An example of a two sub-pixel color space, such asa “slice” of the color space illustrated in FIG. 18, is shown in FIG.20a . Here the x axis 2020 is represented by the emission capability ofa red sub-pixel and the y axis 2010 is represented by the emissioncapability of a green sub-pixel. Notably, any color point within thecolor space represented by the two axes may be emitted by driving thered and the green sub-pixel at levels corresponding to the projection ofthe color point onto each respective sub-pixel. As a more specificexample, a color point 2030 within the color space represented by thered and green color space may be projected onto the red axis as shown byprojection 2032 and may be projected on to the green axis as shown byprojection 2034. The color point 2030 may be emitted by driving the redsub-pixel at a value corresponding to 2033 (i.e., the projection pointof the color point 2030 onto the red sub-pixel axis) and the greensub-pixel at a value corresponding to 2031 (i.e., the projection pointof the color point 2030 onto the green sub-pixel axis). As an example ofa single sub-pixel color space is shown in FIG. 20b . Here, the onlyaxis 2040 corresponds to the emission capability of a red sub-pixel.Notably, any color point within this red pixel's color space may berepresented by a point on the axis 2040. As a specific example, point2045 is a color point that can be emitted by driving the red sub-pixelat the point 2045 itself. It will be understood that the same sub-pixelor sub-pixel type used to show the single sub-pixel color space may be apart of the double and/or triple sub-pixel color space. As a specificexample, a red color pixel may be have the emission capabilityrepresented in FIG. 20b as the red color pixel in FIGS. 20a and 18.

As previously described, a display pixel as disclosed herein may includeat least four sub-pixels. A projection of an original color signal ontoa color space defined by two of the four sub-pixels may be determined.As an example, one way of producing the color specified in an originalcolor signal is to emit a red, green, and blue light from red, green,and blue sub-pixels, respectively. As disclosed herein, alternatively,the original color signal may be projected onto a color space defined bytwo of the sub-pixels such as, for example, the red and the green colorspace. Notably, the projection of the original color signal onto a colorspace defined by two of the sub-pixels may correspond to the magnitudeof emission, corresponding to the two sub-pixels, required to emit theportion of the original color signal corresponding to the twosub-pixels.

FIG. 18 shows an illustrative example of projecting an original colorsignal onto a color space defined by two sub-pixels. As shown in FIG.18, an original color signal may be represented by point 1810. The point1810 may indicate that the original color signal is one that can beemitted by driving the red, green, and blue sub-pixels based on thedirection and magnitude of the point 1810. As disclosed herein, toproduce the specified color using two sub-pixels, a projection of theoriginal color signal onto the color space defined by the red and greensub-pixels, may be determined. This projection may be represented by thefirst projection vector 1802 as shown in FIG. 18. Projecting theoriginal color signal onto the red and green color space may result in acomponent of the original color signal that is based only on the red andgreen color space. In other words, the projection represents thered/green component of the original color signal.

As previously described, a color space also may be defined for a singlesub-pixel. As shown in FIG. 20b , a color space for a single sub-pixelmay be represented by a line as the color space is only singledimensional (as a result of being defined for driving a singlesub-pixel). The color space for a single sub-pixel may be for a primarycolor (e.g., blue, green, red) or may be for a secondary color such asyellow, magenta, cyan, or the like. As an example, a yellow sub-pixelmay have a color space that is a factor of red and green color spaces.As an illustrative example, as shown in FIG. 18, the y-vector 1803represents the color space for a yellow sub-pixel. As shown, the colorspace for the yellow sub-pixel can be represented by points within thered green color space such that the red and/or green sub-pixel may bedriven to emit the color points represented by the yellow color space.

After determining the first projection of the color signal, a secondprojection of the first projection onto a color space defined by asingle sub-pixel may be determined. The color space defined by thesingle sub-pixel may be for a sub-pixel associated with a secondarycolor such that the secondary color is within the color space of twoother sub-pixels in the pixel onto which the first projection wasdetermined. In other words, the color space for the single sub-pixel maybe a combination of at least two other colors emitted by two otherrespective sub-pixels in a pixel. As an example, the second projectionmay be onto a color space defined by a yellow sub-pixel such that thelight emitted by the yellow sub-pixel may be light that is within thecolor space of the red and green sub-pixel. In an illustrative example,as shown in FIG. 18, the color space for a yellow sub-pixel may bedefined by the Y-vector 1804. As shown, the Y-vector 1804 may representthe color space defined by a yellow sub-pixel. The first projectionrepresented by the first projection vector 1802 may have an end at point1811. The first projection vector 1802 may be projected on the Y-vector1804 such that the second projection corresponds to point 1805 on theY-vector 1804.

A second projection of a first projection may represent a singlesub-pixel vector that corresponds to components of both components ofthe two other sub-pixels that the two sub-pixel color space isassociated with. As an example, as shown in FIG. 18, the projection ontothe Y-vector represented by point 1805 represents a color pointassociated with both red and green components of the first projection.In this example, the point 1805 represents the entire green component ofthe first projection vector and represents the entire red component lessthe R-vector 1803 (i.e., RedComponent−R-vector=Red_portion_of_Y-vector).As a more specific example, the point 1811 of the first projectionvector corresponds to a red value of 200 and a green value of 150 (asshown in FIG. 18). The projection of the first projection vector ontothe Y-vector 1804 results in point 1805. Point 1805 on the Y-vectorrepresents the entire green component (i.e., 150) and represents a valueof 100 for the red component. Here, the R-vector may represent theremaining value of 100 such that the overall red value of 200 isrepresented by the R-vector plus the red component of the Y-vector atpoint 1805.

According to embodiments of the disclosed subject matter, a sub-pixelcorresponding to the second projection may be driven based on themagnitude of the second projection. Driving the third sub-pixel based onthe magnitude of the second projection may result in emission of a lightthat is representative of one or more of the components of the firstprojection onto the color space represented by two color pixels.Continuing the previous illustrative example, as shown in FIG. 18, theyellow sub-pixel may be driven based on the magnitude associated withthe second projection point 1805 such that the yellow sub-pixel emitsall of the green component (150) associated with the first projectionvector 1802 and a portion of the red component (100) of the total redcomponent (200) of the first projection vector 1802. Notably, drivingthe yellow sub-pixel at the magnitude associated with the secondprojection may effectively eliminate the need to drive the greensub-pixel as the green component value (150) is emitted by the yellowsub-pixel. Additionally, driving the yellow sub-pixel at the magnitudeassociated with the second projection may effectively reduce theintensity at which the red pixel needs to be driven to produce thedesired color. The reduction may correspond to the magnitude of theR-vector such that, when aggregated, the red component of the yellowemitted light plus the R-vector equal or are substantially close to thered component of the first projected vector. Such a configuration may bemore energy efficient than a conventional three-color arrangement inwhich each of the red, green, and blue sub-pixels would need to bedriven at levels corresponding to the red, green, and blue components ofthe desired color.

More generally, according to embodiments disclosed herein, at least aone sub-pixel in a pixel may not be activated to emit an original colorsignal. For example, as described above, a desired color may be achievedwithout activating a green sub-pixel at all, by using a yellow sub-pixelto obtain the green component of the desired color. As described above,a second sub-pixel may be driven based on the difference between a firstprojection and a second projection, such as the red sub-pixel in theabove example. A third sub-pixel may be driven based on the magnitude ofthe second projection as previously described, such as the yellowsub-pixel in the above example. Finally, a fourth sub-pixel may bedriven based on the respective color component of the original colorsignal. For example, a blue sub-pixel may be driven at a levelcorresponding to the blue component of a color signal in the exampledescribed with respect to FIG. 18. Notably, there may be no need todrive the first sub-pixel at all, since the third sub-pixel can bedriven at a magnitude that includes the necessary color component of thefirst sub-pixel. Additionally, the second sub-pixel may be driven at areduced level as a result of the third sub-pixel being driven at amagnitude that includes at least a portion of the necessary colorcomponent of the second sub-pixel. Notably, the third sub-pixel may emita color equivalent to a combination of colors emitted by the first andsecond sub-pixels.

According to embodiments disclosed herein, an original color signal maybe defined by three primary colors. For example, the original colorsignal may be defined by red, green, and blue coordinates (R, G, B).Each primary color may have a sub-pixel associated with it.Additionally, a secondary sub-pixel may emit light having colorcoordinates (r′, g′, 0) such that it contains components of both R andG. The secondary sub-pixel may be driven at ((G×r′)/g′, G, 0) where(G×r′)/g′ corresponds to the red color component of the original signal(R, G, B) and G corresponds to the entire green component of theoriginal signal. The red sub-pixel may be driven at (R−(G×r′)/g′, 0, 0),where R−(G×r′)/g′ corresponds to the remaining fraction of R such that(G×r′)/g′ and R−(G×r′)/g′ (i.e., the component of the secondarysub-pixel and the component of the red sub-pixel) in combination areequivalent to R, the red component of the original color signal.Accordingly, between the secondary sub-pixel and the red sub-pixel, boththe R and the G component of the original color signal are covered. Thesub-pixel corresponding to a blue emitted color may be driven at (0, 0,B) such that, among the secondary sub-pixel, the red sub-pixel, and theblue sub-pixel, the original color signal (R, G, B) is reproduced.Notably, the green sub-pixel in this example may not be activated toemit the original color signal (R, G, B). Here, the green sub-pixel inthis example may not be activated because g′/r′ is greater than or equalto G/R, which corresponds to the secondary sub-pixel being capable ofemitting the entire green component but not the entire red component.Described another way, in this case the projection onto the green/redcolor space corresponds to a point lying on the “red side” of the“yellow line”, i.e., the side on which the R-vector illustrated in FIG.18 falls.

As another illustrative example, as shown in FIG. 19, an original colorsignal may be represented by vector 1901 and a first projection of theoriginal color signal may be determined onto the color space defined bythe red and green sub-pixels. The first projection may correspond to thefirst projected vector 1902. A second projection onto the Y-vector 1904may be determined and may correspond to the point 1905 on the Y-vector.The point 1905 may correspond to the entire red component of the firstprojected vector 1902 and a fraction of the green component of the firstprojected vector 1902. The entire green component may be represented bythe point 1905 plus the G-vector 1903, as shown in FIG. 19.

According to embodiments disclosed herein, an original color signal maybe defined by three primary colors. For example, the original colorsignal may be defined by red, green, and blue coordinates (R, G, B).Each primary color may have a sub-pixel associated with it.Additionally, a secondary sub-pixel may emit light having colorcoordinates (r′, g′, 0) such that it contains components of both R andG. The secondary sub-pixel may be driven at (R, (R×g′)/r′, 0) where(R×g′)/r′ corresponds to a fraction of G, the green color component ofthe original signal (R, G, B) and R corresponds to the entire redcomponent of the original signal. The green sub-pixel may be driven at(0, G−(R×g′)/r′, 0), where G−(R×g′)/r′ corresponds to the fraction of Gremaining such that (R×g′)/r′ and G−(R×g′)/r′ (i.e., the component ofthe secondary sub-pixel and the component of the green sub-pixel)combine to form G, the green component of the original color signal.Accordingly, among the secondary sub-pixel and the green sub-pixel, boththe R and the G component of the original color signal are covered. Thesub-pixel corresponding to a blue emitted color may be driven at (0, 0,B) such that, between the secondary sub-pixel, the green sub-pixel, andthe blue sub-pixel, the original color signal (R, G, B) is reproduced.Notably, the red sub-pixel in this example may not be activated to emitthe original color signal (R, G, B). Here, the red sub-pixel in thisexample may not be activated because g′/r′ is less than G/R whichcorresponds to the secondary sub-pixel being capable of emitting theentire red component but not the entire green component. This casecorresponds to that in which the projection lies on the “green side” ofthe Y-vector shown in FIG. 19, in contrast to the point illustrated inFIG. 18.

According to an embodiment of the disclosed subject matter, a secondarycolor sub-pixel (e.g., a yellow sub-pixel) may have a color space thatcan be defined by three or more primary colors. As an example, FIG. 20ashows a color point 2030 which corresponds to a red component 2033 and agreen component 2031. Color point 2030 is defined by two primary colors.Similarly, a color space for a sub-pixel may be defined by two primarycolors. As shown in FIG. 18, the color space for the yellow sub-pixel(Y-vector) is defined within the red green color space. The points onthe yellow sub-pixel color space are all within the red green colorspace. Alternatively, if, for example, a color signal is such that itcontains a red component, green component, and a blue component, it maybe originally emitted by three sub-pixels corresponding to primarycolors. Similar to the color signal that is defined by three primarycolors sub-pixels, a color space for a sub-pixel may be defined by threeor more primary colors. The techniques disclosed herein may be appliedby first projecting the color space, for the sub-pixel defined by threeor more primary colors, onto a color space defined by two colors (e.g,the Y-vector in FIG. 18 would be a projection of the yellow sub-pixelscolor space rather than the actual color space itself). The sub-pixeldefined by three or more primary colors may be driven based on the firstand second projections onto the sub-pixel projection. Additionally, twosub-pixels may be operated at reduced values based on driving thesub-pixel defined by three or more primary colors. As an illustrativeexample, a yellow sub-pixel may have a color space defined by red,green, and blue colors. A projection of the yellow sub-pixels colorspace may correspond to the Y-vector shown in FIG. 18. Based on thetechniques disclosed herein, the green sub-pixel may not be activatedand the red sub-pixel may be driven at a reduced level based on drivingthe yellow sub-pixel at a magnitude associated with a projection ontothe Y-vector. Additionally, the blue sub-pixel may operate at a reducedlevel based on the difference between the yellow sub-pixel's color spaceand the Y-vector (i.e., the projection of the yellow sub-pixel's colorspace onto the red-green color space).

If an original color signal is within the color space of two sub-pixels(i.e., instead of three sub-pixels), only a first projection may beneeded and the original color signal may be emitted using only twosub-pixels. Here, a secondary sub-pixel color space may also becontained within the color space of the same two sub-pixels that theoriginal color signal is in. Accordingly, the original color signal maybe projected onto the color space of the secondary sub-pixel. Thesecondary sub-pixel may be driven based on the magnitude of theprojection. The secondary sub-pixel may be driven such that it containsan entire first color component of the original color signal and aportion of a second color component of the original signal. A differentsub-pixel may be driven to compensate for the remaining portion of thesecond color component of the original signal. Accordingly, only thesecondary sub-pixel and the other sub-pixel may be driven of the atleast four sub-pixels within the pixel.

It will be understood that at any given color signal, a given sub-pixelmay be activated or not activated based on the color signal. As anexample, using the notation introduced previously, when g′/r′ is greaterthan or equal to G/R, then a green sub-pixel may not be activatedwhereas when it is less than G/R, a red sub-pixel may not be activated.It will be understood that for two different color signals, a givensub-pixel may be active or not active. It will also be understood thatalthough colors such as red, green, blue, yellow, magenta, and cyan aredisclosed herein, the techniques disclosed herein may be applied to anycolor signals and/or sub-pixels associated with any colors.

As used herein, various components may be used as color altering layersas disclosed. Suitable components include color conversion layers, colorfilters, color changing layers, microcavities, and the like. The dyesused in color conversion layers as disclosed herein are not particularlylimited, and any compounds may be used as long as the compound iscapable of converting color of light emitted from a light source to arequired color, which is basically a wavelength conversion elementcapable of converting the wavelength of the light from the light sourceto a wavelength 10 nm or more longer than that of the light of the lightsource. It may be an organic fluorescent substance, an inorganicfluorescent substance, or a phosphorescent substance, and may beselected according to the objective wavelength. Examples of the materialinclude, but not limit to the following classes: xanthen, acridine,oxazine, polyene, cyanine, oxonol, benzimidazol, indolenine, azamethine,styryl, thiazole, coumarin, anthraquinone, napthalimide,aza[18]annulene, porphin, squaraine, fluorescent protein,8-hydroxyquinoline derivative, polymethin, nanocrystal, protein,perylene, phthalocyanine and metal-ligand coordination complex.

Examples of the fluorescent dye for converting luminescence of from UVand higher energy light to blue light include, but not limit to thestyryl-based dyes such as 1,4-bis(2-methylstyryl)benzene, andtrans-4,4′-diphenylstilbene, and coumarin based dyes such as7-hydroxy-4-methylcoumarin, and combinations thereof.

Examples of the fluorescent dye for converting luminescence of from bluelight to green light include, but not limit to the coumarin dyes such as2,3,5,6-1H,4H-tetrahydro-8-trifluoromethylquinolizino(9,9a,1-gh)coumarin, 3-(2′-benzothiazolyl)-7-diethylaminocoumarin,3-(2′-benzimidazolyl)-7-N,N-diethylaminocoumarin, and naphthalimide dyessuch as Basic Yellow 51, Solvent yellow 11 and Solvent Yellow 116, andpyrene dyes such as 8-Hydroxy-1,3,6-pyrenetrisulfonic acid trisodiumsalt (HPTS), and combinations thereof.

Examples of the fluorescent dye for converting luminescence of from blueto green light to red include, but not limit to the perylene based dyessuch asN,N-bis(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxdiimide(Lumogen Red F300), cyanine-based dyes such as4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl-4H-pyran,pyridine-based dyes such as1-ethyl-2-(4-(p-dimethylaminophenyl)-1,3-butadienyl)-pyridiniumperchlorate, and rhodamine-based dyes such as Rhodamine Band Rhodamine6G, and oxazine-based dyes, and combinations thereof.

Examples of the inorganic fluorescent substance include, but not limitto an inorganic fluorescent substance comprising a metal oxide or metalchalcogenide doped with a transition metal ion, including a rare-earthmetal ion.

Many metal-ligand coordination complexes can be used as dyes, they canbe both fluorescent and phosphorescent substance.

It may be preferred to use a color conversion layer in the state thatthe layer is stacked on a color filter. The stacked structure thereof onthe color filter makes it possible to make better color purity of lighttransmitted through the color conversion layer. In some configurations,a “color altering layer” as disclosed herein may include multiplecomponents, such as a color filter disposed in a stack with a colorconversion layer, or just a color conversion layer alone, or just acolor filter alone.

The material used for color filters is not particularly limited. Afilter may be made of, for example, a dye, a pigment and a resin, oronly a dye or pigment. The color filter made of a dye, a pigment and aresin may be a color filter in the form of a solid wherein the dye andthe pigment are dissolved or dispersed in the binder resin.

Examples of the dye or pigment used in the color filter include, but notlimit to perylene, isoindoline, cyanine, azo, oxazine, phthalocyanine,quinacridone, anthraquinone, and diketopyrrolo-pyrrole, and combinationsthereof.

As used herein, and as would be understood by one of skill in the art, a“color conversion layer” (e.g. a “down conversion layer”) may comprise afilm of fluorescent or phosphorescent material which efficiently absorbshigher energy photons (e.g. blue light and/or yellow light) and reemitsphotons at lower energy (e.g. at green and/or red light) depending onthe materials used. That is, the color conversion layer may absorb lightemitted by an organic light emitting device (e.g. a white OLED) andreemit the light (or segments of the wavelengths of the emissionspectrum of the light) at a longer wavelength. A color conversion layermay be a layer formed by mixing the fluorescent medium materialcontained in the above-mentioned color conversion layer with the colorfilter material. This makes it possible to give the color conversionlayer a function of converting light emitted from an emitting device andfurther a color filter function of improving color purity. Thus, thestructure thereof is relatively simple.

Embodiments disclosed herein may be incorporated into a wide variety ofproducts and devices, such as flat panel displays, smartphones,transparent displays, flexible displays, televisions, portable devicessuch as laptops and pad computers or displays, multimedia devices, andgeneral illumination devices. Displays as disclosed herein also may haverelatively high resolutions, including 250 dpi, 300 dpi, 350 dpi, ormore.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

The invention claimed is:
 1. A method of driving a display pixelcomprising at least four sub-pixels, the method comprising: determininga first projection of an original color signal onto a color spacedefined by a first and second sub-pixel of the at least four sub-pixels;determining a second projection of the first projection onto a secondcolor space defined by a third sub-pixel; driving the third sub-pixelbased on the magnitude of the second projection; driving the secondsub-pixel based on the difference between the first projection and thesecond projection; and driving the fourth sub-pixel based on a componentof the original color signal; wherein the first sub-pixel is notactivated while driving the third sub-pixel based on the magnitude ofthe second projection and driving the second sub-pixel based on thedifference between the first projection and the second projection. 2.The method of claim 1, wherein the third sub-pixel emits a colorequivalent to a combination of colors emitted by the first and secondsub-pixels.
 3. The method of claim 1, wherein the first sub-pixel is agreen sub-pixel.
 4. The method of claim 1, wherein the first sub-pixelis a red sub-pixel.
 5. The method of claim 1, wherein the thirdsub-pixel is one selected from the group consisting of: a yellowsub-pixel, a magenta sub-pixel, and a cyan sub-pixel.
 6. The method ofclaim 1, wherein the original color signal is defined by (R, G, B) colorcoordinates and wherein the third sub-pixel emits light having colorcoordinates at (r′, g′, 0).
 7. The method of claim 6, wherein the thirdsub-pixel is driven at ((G×r′)/g′, G, 0), the second sub-pixel is drivenat (R−(G×r′)/g′, 0, 0), the first sub-pixel is driven at (0, 0, 0), andthe fourth sub-pixel is driven at (0, 0, B).
 8. The method of claim 7,wherein g′/r′ is greater than or equal to G/R.
 9. The method of claim 6,wherein the third sub-pixel is driven at (R, (R×g′)/r′, 0) the secondsub-pixel is driven at (0, 0, 0), the first sub-pixel is driven at (0,G−(R×g′)/r′, 0), and the fourth sub-pixel is driven at (0, 0, B). 10.The method of claim 7, wherein g′/r′ is less than G/R.
 11. The method ofclaim 1, wherein the at least four sub-pixels comprise an emissiveregion.
 12. The method of claim 11, wherein the emissive region containstwo or fewer colors.
 13. The method of claim 1, wherein the sub-pixelsare arranged in a pixel arrangement comprising no more than two coloraltering layers.
 14. The method of claim 1, further comprising:determining a third projection of a second original color signal onto acolor space defined by the first and second sub-pixel of the at leastfour sub-pixels; determining a fourth projection, of the thirdprojection, onto the second color space defined by a third sub-pixel;driving the third sub-pixel based on the magnitude of the fourthprojection; driving the first sub-pixel based on the difference betweenthe first projection and the second projection; and driving the fourthsub-pixel based on a component of the original color signal; wherein thesecond sub-pixel is not activated while driving the third sub-pixelbased on the magnitude of the second projection and driving the firstsub-pixel based on the difference between the first projection and thesecond projection.
 15. A device comprising a display pixel, wherein thedevice is configured to operate the display pixel by: determining afirst projection of an original color signal onto a color space definedby a first and second sub-pixel of the at least four sub-pixels;determining a second projection of the first projection onto a secondcolor space defined by a third sub-pixel; driving the third sub-pixelbased on the magnitude of the second projection; driving the secondsub-pixel based on the difference between the first projection and thesecond projection; and driving the fourth sub-pixel based on a componentof the original color signal; wherein the first sub-pixel is notactivated while driving the third sub-pixel based on the magnitude ofthe second projection and driving the second sub-pixel based on thedifference between the first projection and the second projection. 16.The device of claim 15, wherein the at least four sub-pixels comprise anemissive region.
 17. The device of claim 16, wherein the emissive regioncontains two or fewer colors.
 18. The device of claim 15, wherein thesub-pixels are arranged in a pixel arrangement comprising no more thantwo color altering layers.
 19. A method of driving a display pixelcomprising at least four sub-pixels, the method comprising: determininga first projection of a third sub-pixel color space onto a color spacedefined by a first and second sub-pixel of the at least four sub-pixels;determining a second projection of an original color signal onto a colorspace defined by a first and second sub-pixel of the at least foursub-pixels; determining a third projection of the second projection ontothe first projection; driving the third sub-pixel based on the magnitudeof the third projection; driving the second sub-pixel based on thedifference between the second projection and the third projection; anddriving the fourth sub-pixel based on a component of the original colorsignal and the difference between the third sub-pixel color space andthe first projection; wherein the first sub-pixel is not activated whiledriving the third sub-pixel based on the magnitude of the thirdprojection and driving the second sub-pixel based on the differencebetween the second projection and the third projection.
 20. A method ofdriving a display pixel comprising at least four sub-pixels, the methodcomprising: determining a first projection of an original color signalonto a color space defined by a third sub-pixel; driving the thirdsub-pixel based on the magnitude of the first projection; driving asecond sub-pixel based on the difference between the original colorsignal and the first projection; and wherein the first sub-pixel and thefourth sub-pixel are not activated while the third sub-pixel is drivenbased on the magnitude of the third projection and second sub-pixel isdriven based on the difference between the original color signal and thefirst projection.